1. Field of the Invention
The present invention relates to a double-cylinder type dielectric barrier discharge lamp and a dry cleaning device which uses a dielectric barrier discharge lamp as the ultraviolet light source, and particularly for dry cleaning device, relates to a dry cleaning device with which the organic substances adhering to the surface of a workpiece, such as a semiconductor wafer, are decomposed by projecting the ultraviolet light itself or exposing the workpiece to the ozone generated with the ultraviolet light.
2. Description of the Prior Art
The dry cleaning device with which ultraviolet light is projected onto a workpiece, such as a semiconductor wafer, or the workpiece is exposed to the ozone generated when the ultraviolet light permeates the air or gas oxygen, for decomposing and removing the organic substances adhering to the surface of the workpiece has been conventionally used in the semiconductor manufacturing process and the like. Some dry cleaning devices use not only either ultraviolet light or ozone, but also both ultraviolet light and ozone for promotion of decomposition of the organic substances.
As an ultraviolet light source for use with a dry cleaning device, a variety of discharge lamps, such as a mercury lamp, are widely known. Being a type of discharge lamp, the dielectric barrier discharge lamp which uses xenon as the principal component of the discharge gas radiates ultraviolet light having a wavelength as short as 172 nm. The ultraviolet light with a short wavelength has high power, being excellent in ability to decompose an organic substance, and thus can be advantageously used as cleaning power for a dry cleaning device, therefore, the dielectric barrier discharge lamp is excellent as the ultraviolet light source for a dry cleaning device.
The dielectric barrier discharge lamp is described in Japanese Unexamined Patent Publication No. 7(1995)-272693, for example. The cleaning device which uses a dielectric barrier discharge lamp as the ultraviolet light source is disclosed in Japanese Patent Publication No. 2705023, for example. In FIG. 11 in this Japanese Patent Publication No. 2705023, a tabular light source device is shown as the ultraviolet light source for a dry cleaning device. With the tabular light source device as shown in FIG. 11 in Japanese Patent Publication No. 2705023, double-cylinder type dielectric barrier discharge lamps (33a, 33b, 33c) are disposed side by side in the recess (4) of a lunch-box type metallic container (30) which also serve as a light reflecting plate. The metallic container (30) is of tabular type, one wide surface being provided as an open surface. The open surface is covered with a light taking-out window (31) made of a synthetic quartz glass plate. Into the recess (4) of the metallic container (30), nitrogen (N2) gas is fed at a rate of a few liters per minute. In the air, ultraviolet light is contacted with oxygen, and converts it into ozone, therefore, by filling the recess (4) with nitrogen (N2) gas in place of air, attenuation of the ultraviolet light and generation of ozone in the metallic container (30) are prevented. With this double-cylinder type dielectric barrier discharge lamp (33a, 33b, 33c), a net-like outside electrode (20a, 20b, 20c) is exposed, therefore, if ozone is generated in the recess (4), the outside electrode (20a, 20b, 20c) will be oxidized, and deteriorated, but by filling the recess (4) with nitrogen (N2) gas, generation of ozone is prevented, and thus deterioration of the outside electrode (20a, 20b, 20c) is suppressed.
The tabular light source device as shown in FIG. 11 in the above-mentioned Japanese Patent Publication No. 2705023 is used as the ultraviolet light source (100) for the dry cleaning device as shown in FIG. 2 in the same Japanese Patent Publication or the like. With the dry cleaning device as shown in FIG. 2 in Japanese Patent Publication No. 2705023, the ultraviolet light source (100) and a substance to be treated (a substance from which the organic contamination adhering to the surface is removed, being oxidized by the ultraviolet light or ozone, i.e., a workpiece, which is here a slide glass (9)) are disposed in a treatment chamber (7). The ultraviolet light source (100) is held at a level of xe2x80x9cdxe2x80x9d above the top of the workpiece (9). Into the treatment chamber (7), a gas mixture of nitrogen (N2) gas and oxygen (O2) gas are supplied. The ultraviolet light radiated from the dielectric barrier discharge lamp permeates the nitrogen (N2) gas in the ultraviolet light source (100), further permeates the quartz glass of the taking-out window in the ultraviolet light source (100), and permeates the gas mixture of nitrogen (N2) gas and oxygen (O2) gas in the treatment chamber (7), being projected onto the top of the workpiece (9). Ozone offers a strong oxidation action, thus is used in conjunction with the ultraviolet light for cleaning the workpiece (9).
In FIG. 7 in the above-mentioned Japanese Patent Publication No. 2705023, an example of double-cylinder type dielectric barrier discharge lamp is given in detail. The discharge lamp (18) in this double-cylinder type dielectric barrier discharge lamp is made of quartz glass, and is in the shape of a hollow cylinder, an inner tube (23) and an outer tube (24) being provided coaxially. A metallic electrode (20), which is the outside electrode, is provided on the outer surface of the outer tube (24), being formed in a net-like shape to allow permeation of the light. The outside electrode (20) is coated with an antioxidizing coating (22). An electrode (19), which is the inside electrode, comprises an aluminum film formed on the outer surface (the circumferential wall) of the inner tube (23), which also serves a reflection coating. The space between the inner tube (23) and the outer tube (24) provides a discharge space (21), which is filled with xenon as a discharge gas. The discharge container (18) has an overall length of 100 mm with the inner tube (23) having an outside diameter of 6 mm, and the outer tube (24) having an inside diameter of 8 mm.
FIG. 7 in Japanese Unexamined Patent Publication No. 7(1995)-272693 gives another example of dielectric barrier discharge lamp. The dielectric barrier discharge lamp as shown in FIG. 7 in Japanese Unexamined Patent Publication No. 7(1995)-272693 is called an aperture type one, having an outside electrode (8) made of aluminum which also serves as a light reflecting plate, being provided on a part of the circumferential surface of a discharge container (1). The region of the discharge container (1) which has no outside electrode provides a light taking-out window (9). The light taking-out window (9) extends in the longitudinal direction of the lamp, being formed in a slit-like shape.
To dissipate the heat generated in the dielectric barrier discharge lamp, air cooling by means of a fan and water cooling by passing the water through the cooling water tube provided inside of the discharge container.
However, providing a cooling fan or a cooling water supply device separately results in a complicated, large-sized, and expensive lamp device as an ultraviolet light source, making the maintenance cumbersome, and lowering the reliability.
A dielectric barrier discharge lamp must be provided with a means for preventing the electrode from being oxidized by the ozone generated by the ultraviolet light acting on the oxygen (O2) gas. With the dielectric barrier discharge lamp as shown in FIG. 7 in the above-mentioned Japanese Patent Publication No. 2705023, the outside electrode (20) is coated with an anti-oxidizing coating (22). Further, with the tabular light source device as shown in FIG. 11 in the same Japanese Patent Publication, the dielectric barrier discharge lamp is housed in the chamber filled with nitrogen (N2) gas. But, with the aperture type dielectric barrier discharge lamp as shown in FIG. 7 in Japanese Unexamined Patent Publication No. 7(1995)-272693, no means for prevention of electrode oxidation is shown.
To equip a dry cleaning device with a dielectric barrier discharge lamp, the cleaning chamber structure must be connected with the dielectric barrier discharge lamp for projecting the ultraviolet light into the cleaning chamber, and providing the above-mentioned cooling means and a means for prevention of electrode oxidation for the dielectric barrier discharge lamp tends to make the construction of the cleaning device as a whole intricate. However, no dielectric barrier discharge lamps which is simple in construction, while being provided with both cooling means and electrode oxidation prevention means have not been disclosed.
When the dielectric barrier discharge lamp as shown in FIG. 11 in the above-mentioned Japanese Patent Publication No. 2705023 is used as the ultraviolet light source (100) for the dry cleaning device as shown in FIG. 2 in Japanese Patent Publication No. 2705023, the media through which the ultraviolet light radiated from the lamp permeates before reaching the workpiece (9) act as follows: The ultraviolet light radiated from the dielectric barrier discharge lamp in the ultraviolet light source (100) permeates the nitrogen (N2) gas in the ultraviolet light source (100), further permeates the quartz glass of the taking-out window in the ultraviolet light source (100), and permeates the gas mixture of nitrogen (N2) gas and oxygen (O2) gas in the treatment chamber (7), being projected onto the top of the workpiece (9). Thus, with this cleaning device, the ultraviolet light permeates both the gas mixture of nitrogen (N2) gas and oxygen (O2) gas and the quartz glass, which are different in index of refraction. In other words, the ultraviolet light permeating media are not uniform. Then, the ultraviolet light radiated from the dielectric barrier discharge lamp is partially reflected at the surface of the quartz glass window, and partially absorbed in the inside of the quartz glass window. The absorption factor of the inside of the quartz glass window varies depending upon the thickness t, and is approx. 5% when the thickness t is 1 mm, approx. 30% when the thickness t is 10 mm, and approx. 65% when the thickness t is 20 mm.
When the outside electrode of the double-cylinder type dielectric barrier discharge lamp is of net-like shape, being wound around the circumference of the discharge container, there occurs a loss according to the opening ratio, which is the ratio of the area of the hole portion of the net-like electrode to that of the metallic portion. The opening ratio loss ranges from a few percent to a few tens percent.
When the tabular light source device as shown in FIG. 11 in the above-mentioned Japanese Patent Publication No. 2705023 is used with the dry cleaning device, the dielectric barrier discharge lamp is housed in the chamber filled with nitrogen (N2) gas, and therefore the electrode is not exposed to the ozone, which allows the electrode to be prevented from being oxidized, however, while the ultraviolet light radiated from the dielectric barrier discharge lamp reaches the light taking-out window (31) made of quartz glass, the ultraviolet light is diffused. Therefore, with the dry cleaning device which uses the tabular light source device as shown in FIG. 11 in the above-mentioned Japanese Patent Publication No. 2705023 as the ultraviolet light source, the ultraviolet light radiated from the dielectric barrier discharge lamp is attenuated before being projected onto the workpiece, compared to a dry cleaning device with which the dielectric barrier discharge lamp is directly faced to the cleaning chamber with the light taking-out window (31) made of quartz glass being removed.
To maintain the mechanical strength of the light taking-out window made of quartz glass, the quartz glass window must be thick in proportion to the area thereof. To increase the cleaning efficiency by cleaning a number of wafers at once, the area of the cleaning chamber must be widened, and in proportion to the area of the cleaning chamber, the area of the quartz glass window must be increased, which logically requires the thickness of the quartz glass window to be increased. With the increase in thickness of the quartz glass window, the absorption factor is increased, resulting in an increase in loss of the ultraviolet light. In addition, the quartz glass window is expensive, and yet, the permeability of light is decreased with the use, which means that it is an expendable item. Thus, an increase in area and thickness of the quartz glass window can be a great factor of increase in manufacturing cost of the dry cleaning device.
In addition, with the tabular light source device as shown in FIG. 11 in Japanese Patent Publication No. 2705023, the metallic container (30) for housing the dielectric barrier discharge lamp (33a, 33b, 33c) also serves as a light reflecting plate. With this dry cleaning device, the light reflecting structure must be large-sized, which prevents the cleaning device as a whole from being compact.
To solve the above-stated problems, the present invention offers the following means:
(1) A double-cylinder type dielectric barrier discharge lamp which has a double-cylinder type discharge container which seals the discharge gas, such as xenon gas, in the space between a transparent outside cylindrical tube and inside cylindrical tube; an outside electrode provided in the vicinity of the outside of the outside cylindrical tube; and an inside electrode which is coaxially disposed in the bore of the inside cylindrical tube; comprising:
a gas introduction tube which has an outside diameter smaller than the diameter of the bore of said inside cylindrical tube, providing a clearance between it and the bore, and is inserted into the bore;
an other-end-side end-structure which seals the opening of said bore on the other end side so that gas, such as, nitrogen gas which is introduced from the opening at one end of said gas introduction tube and discharged from the opening at the other end of the gas introduction tube is turned back on the other end side to be introduced into said clearance; and
a cover which covers said outside electrode, and prevents the outside electrode from being exposed to the ozone generated by the ultraviolet light radiated from said discharge container;
wherein said outside electrode is formed in a trough-like shape, and is disposed with the inner surface being tightly contacted with the O.D. surface of said outside cylindrical tube,
said inner surface forms a circular arc, such as a semicircle, in the plane orthogonalizing the axis of said outside cylindrical tube, and provides a mirror surface which reflects the light,
said inside electrode is disposed in the clearance between said gas introduction tube and said inside cylindrical tube, being formed in a net-like shape which allows said gas to flow along the axial direction in the clearance, and
said outside cylindrical tube provides a light taking-out window of said discharge container in the region corresponding to the aperture of said outside electrode.
(2) A dielectric barrier discharge lamp according to the above paragraph (1),
wherein said cover is formed in the shape which forms a cooling gas space for passing gas between the cover and said outside electrode for cooling the outside electrode,
an one-end-side end-structure which seals the opening of said bore on said one end side so that said gas discharged from said clearance on said one end side is introduced into said cooling gas space is provided, and
a gap for discharging said gas passed through said cooling gas space is formed between the O.D. surface of said outside cylindrical tube or the outer surface of said outside electrode and said cover 3.
(3) A dielectric barrier discharge lamp according to the above paragraph (2),
wherein said inner surface of said outside electrode forms a semicircle in the plane orthogonalizing the axis of the outside cylindrical tube,
the sectional shape of said cover in the plane orthogonalizing said axis is of letter-Π, and
said gap is formed between the edge along the direction of said axis of said outside electrode and the edge of the Π-shaped opening of said cover.
(4) A tabular light source device with which a plurality of dielectric barrier discharge lamps according to the above paragraphs (1) to (3) are tabularly arranged, wherein the axes of the plurality of dielectric barrier discharge lamps are parallel to one another, said light taking-out windows in the plurality of dielectric barrier discharge lamps are directed toward the same side, and the sides of said covers are contacted to one another or a spacer is interposed between covers.
(5) A dry cleaning device, having an ultraviolet light source which comprises a dielectric barrier discharge lamp according to the above paragraphs (1) to (3) or a tabular light source device according to the above paragraph (4), and a cleaning chamber structure for accommodating a workpiece,
wherein, with said cleaning chamber structure, the workpiece is exposed to at least either of the ultraviolet light projected from said ultraviolet light source and the ozone generated by the ultraviolet light acting on the oxygen gas, and
said ultraviolet light projected from said light taking-out window reaches said workpiece through a medium having a uniform index of refraction.
(6) A dry cleaning device according to the above paragraph (5), wherein, with said cleaning chamber structure, the cleaning surface of said workpiece is located at a distance as small as a few mm from said light taking-out window.
(7) A dry cleaning device, having an ultraviolet light source which comprises a tabular light source device, and a cleaning chamber structure for accommodating a workpiece,
wherein, with said cleaning chamber structure, the workpiece is exposed to at least either of the ultraviolet light projected from said ultraviolet light source and the ozone generated by the ultraviolet light acting on the oxygen gas,
said tabular light source device comprises a plurality of dielectric barrier discharge lamps according to the above paragraph (3) which are tabularly arranged side by side with the sides of said covers being contacted to one another or a spacer being interposed between covers, and said light taking-out windows in the plurality of dielectric barrier discharge lamps are directed toward the same side,
said gap is opened into the cleaning chamber of said cleaning chamber structure, and
said ultraviolet light projected from said light taking-out window reaches said workpiece through a medium having a uniform index of refraction.
(8) A dry cleaning device according to the above paragraph (7), wherein, with said cleaning chamber structure, the cleaning surface of said workpiece is located at a distance as small as a few mm from said light taking-out window.
One purpose of the present invention is to offer a dielectric barrier discharge lamp which is simple in construction while being provided with both cooling means and electrode oxidation prevention means, and can direct the ultraviolet light toward a definite direction with no need for a special construction for reflection of ultraviolet light. The other purpose of the present invention is to offer a dry cleaning device using a dielectric barrier discharge lamp as the ultraviolet light source with which the electrode of the dielectric barrier discharge lamp can be insulated from ozone without using an ultraviolet light taking-out window made of quartz glass.